1. Technical Field
The present invention relates generally to radio frequency (RF) devices. More particularly, the present invention relates to RF multi-port switches.
2. Related Art
Complex, multi-function electronic devices are comprised of many interconnected modules and components, each of which serves a dedicated purpose. As a general example, wireless communication devices may be comprised of a transmit chain and a receive chain, with the antenna and the transceiver circuit being a part of both the transmit chain and receive chain. The transmit chain may additionally include a power amplifier for increasing the output power of the generated RF signal from the transceiver, while the receive chain may include a low noise amplifier for boosting the weak received signal so that information can be accurately and reliably extracted therefrom.
The low noise amplifier and the power amplifier may together comprise a front end module or front end circuit, which also includes an RF switch circuit that selectively interconnects the power amplifier and the low noise amplifier to the antenna. The connection to the antenna is switched between the receive chain circuitry, i.e., the low noise amplifier and the receiver, and the transmit chain circuitry, i.e., the power amplifier and the transmitter. In time domain duplex communications systems where a single antenna is used for both transmission and reception, this switching between the receive chain and the transmit chain occurs rapidly many times throughout a typical communications session. Besides RF communications systems, switches and switch circuits find application in many other contexts.
The RF switches and the amplifier circuits of the front end module are manufactured as an integrated circuit. In high-power applications such as GSM (Global System for Mobile communications) handsets, WLAN (wireless local area networking) client interface devices and infrastructure devices, the integrated circuits are typically manufactured with a GaAs (gallium arsenide) semiconductor substrate. The SOI (silicon-on-insulator) process has also found use in RF switch circuit applications, though spurious emissions due to the necessity of charge pumps can adversely affect receive chain sensitivity in many communication systems. Good insertion loss and isolation are possible with both GaAs and SOI processes, but manufacturing costs tend to be higher in comparison to more conventional semiconductor technologies such as the CMOS (Complementary Metal Oxide Semiconductor) process. There have been several attempts to implement RF switches on the CMOS process, but only low power devices have been realized thus far. This is, in part, due to the parasitic capacitance of transistors and low substrate resistance of bulk semiconductor wafers used in the CMOS process. Accordingly, high isolation and linearity at large signal levels have been difficult to achieve.
An RF switch has several performance parameters, including insertion loss, isolation, return loss, and linearity. Insertion loss refers to the power lost in the RF switch, and is expressed in dB. It is defined by Pout−Pin (dB), where Pin is the input power applied to the RF switch, and Pout is the power at the output port of the RF switch. Isolation refers to the measure of signal attenuation, expressed in dB, between the active signal port and the inactive signal port. Additionally, return loss refers to the measure of input and/or output matching conditions, and is expressed in dB. Linearity, or power handling capability, is the capability of the RF switch to minimize distortion at high power output levels and is expressed in dBm. It is typically represented by the 1 dB compression point (P1 dB), or the point at which insertion loss is degraded by 1 dB.
Accordingly, there is a need in the art for improved RF multi-port switches, whether single pole-double throw, single pole-triple throw, dual port-dual throw, or any other switch type. Furthermore, there is a need in the art for RF multi-port switches that can be implemented on CMOS substrates or any other semiconductor technology while minimizing insertion loss, return loss, and spurious emissions, and maximizing isolation and linearity even at low control and bias voltages.